Already known from the practice are motor vehicles having automatic transmission torque converter lock-up clutches which can be operated in an "opened" or "activated" state. The "activated" state comprises of the regulated slipping and closed state.
Such a torque converter lock-up clutch has been described, for example, in ATZ Automobiltechnische Zeitschrift 96 (1994) 11. The most important input variables for the regulator of said known torque converter lock-up clutch are the engine speed of rotation and the turbine speed of rotation. By subtraction of those two input variables, the torque converter slip is computed as the regulating variable. The command variable WK nominal slip is laid down in a performance graph in an electronic transmission controller (EGS).
An electric pressure regulator (EDS) serves the actuator for the pressure control of said torque converter lock-up clutch, which, in turn, is controlled by the electronic transmission controller (EGS) via a current-regulated final step. The EDS converts the preset control current according to its characteristic line to a proportional hydraulic pressure. By said EDS, for example, in a 2-line torque converter with two control valves, both the torque converter pressure, which acts upon the rear side of the torque converter clutch piston, and the torque converter clutch pressure which closes the torque converter clutch piston, are controlled.
The torque converter lock-up clutch is designated as "open" or "opened" when no torque is transmitted via the torque converter lock-up clutch.
In an "activated" state the piston of the torque converter lock-up clutch is loaded with pressure. One or more friction disc(s) are compressed by the resulting piston force and a corresponding transmission torque is produced.
In the so-called "quick opening" of the torque converter lock-up clutch, the torque transmitted by the torque converter lock-up clutch is quickly broken down to low values (for example, &lt;50 Nm) or the torque converter lock-up clutch is completely opened.
Together with the usual control functions, said torque converter lock-up clutch has different special functions in order to optimize the properties.
Thus, in this torque converter lock-up clutch, a process is known in which the torque converter lock-up clutch is always open below a threshold temperature, and in which during the warm up the nominal slip is raised in comparison with the normal operation.
By another control process, the operation of the torque converter lock-up clutch is eliminated during very elevated transmission temperatures in order to protect the friction areas against overheating.
In addition, a process for quick filling is known where the piston of the torque converter lock-up clutch, in the transition from open to regulated state, is moved to the regulating position.
By another switching process, the operation of the torque converter lock-up clutch is maintained even during a gearshift in order to prevent a high rotation of the engine wherein the nominal slip is raised during a gearshift.
However, certain driving situations are not correctly detected by the known torque converter lock-up clutch and the electronic transmission controller thereof, resulting in the known torque converter lock-up clutch remaining, for example, "activated" even though it should have been opened.
Such a driving situation is the spinning of the driving wheels of a vehicle on a smooth ground, while the torque converter lock-up clutch is activated, and the subsequent transition to a ground of high frictional value. When the driving wheels spin, in the known torque converter lock-up clutches, a switch is made to a next higher gear. When the driving wheels again contact the rough ground, they are abruptly decelerated, but because of the spinning of the driving wheels too high of a gear has been switched in by the automatic transmission with the known activated torque converter lock-up clutch. That situation can result in the engine becoming stalled from the rigid through drive between the input and the wheels, and thus ensues a drive situation critical to safety.
Therefore, the problem on which this invention is based is to make available a process by which the state of a torque converter lock-up clutch in an automatic transmission is tuned to the quick deceleration of the driving wheels of a vehicle.